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          <h1 class="post-title" itemprop="name headline">谈谈golang的netpoll原理(二)</h1>
        

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        <p>接上文我们查看了bind和listen流程，直到了listen操作会在内核初始化一个epoll表，并将listen的描述符加入到epoll表中</p>
<h2 id="如何保证epoll表初始化一次"><a href="#如何保证epoll表初始化一次" class="headerlink" title="如何保证epoll表初始化一次"></a>如何保证epoll表初始化一次</h2><p>前文我们看到pollDesc的init函数中调用了runtime的pollOpen函数完成的epoll创建和描述符加入，这里再贴一次代码<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(pd *pollDesc)</span> <span class="title">init</span><span class="params">(fd *FD)</span> <span class="title">error</span></span> &#123;</span><br><span class="line">	serverInit.Do(runtime_pollServerInit)</span><br><span class="line">	ctx, errno := runtime_pollOpen(<span class="keyword">uintptr</span>(fd.Sysfd))</span><br><span class="line">	<span class="keyword">if</span> errno != <span class="number">0</span> &#123;</span><br><span class="line">		<span class="keyword">if</span> ctx != <span class="number">0</span> &#123;</span><br><span class="line">			runtime_pollUnblock(ctx)</span><br><span class="line">			runtime_pollClose(ctx)</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">return</span> errnoErr(syscall.Errno(errno))</span><br><span class="line">	&#125;</span><br><span class="line">	pd.runtimeCtx = ctx</span><br><span class="line">	<span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>runtime_pollServerInit link的是runtime/netpoll.go中的poll_runtime_pollServerInit函数<br>由于serverInit是sync.Once类型，所以runtime_pollServerInit只被初始化一次，而epoll模型的初始化就是在该函数完成<br><a id="more"></a><br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">poll_runtime_pollServerInit</span><span class="params">()</span></span> &#123;</span><br><span class="line">	netpollGenericInit()</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">netpollGenericInit</span><span class="params">()</span></span> &#123;</span><br><span class="line">	<span class="keyword">if</span> atomic.Load(&amp;netpollInited) == <span class="number">0</span> &#123;</span><br><span class="line">		lock(&amp;netpollInitLock)</span><br><span class="line">		<span class="keyword">if</span> netpollInited == <span class="number">0</span> &#123;</span><br><span class="line">			netpollinit()</span><br><span class="line">			atomic.Store(&amp;netpollInited, <span class="number">1</span>)</span><br><span class="line">		&#125;</span><br><span class="line">		unlock(&amp;netpollInitLock)</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>netpollinit实现了不同模型的初始化，epoll的实现在runtime/netpoll_epoll.go中<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">netpollinit</span><span class="params">()</span></span> &#123;</span><br><span class="line">	epfd = epollcreate1(_EPOLL_CLOEXEC)</span><br><span class="line">	<span class="keyword">if</span> epfd &lt; <span class="number">0</span> &#123;</span><br><span class="line">		epfd = epollcreate(<span class="number">1024</span>)</span><br><span class="line">		<span class="keyword">if</span> epfd &lt; <span class="number">0</span> &#123;</span><br><span class="line">			<span class="built_in">println</span>(<span class="string">"runtime: epollcreate failed with"</span>, -epfd)</span><br><span class="line">			throw(<span class="string">"runtime: netpollinit failed"</span>)</span><br><span class="line">		&#125;</span><br><span class="line">		closeonexec(epfd)</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">//...</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>可以看到上述代码里实现了epoll模型的初始化，所以对于一个M主线程只会初始化一张epoll表，所有要监听的文件描述符都会放入这个表中。</p>
<h2 id="跟随accept看看goroutine挂起逻辑"><a href="#跟随accept看看goroutine挂起逻辑" class="headerlink" title="跟随accept看看goroutine挂起逻辑"></a>跟随accept看看goroutine挂起逻辑</h2><p>当我们调用Listener的Accept时，Listener为接口类型，实际调用的为TCPListener的Accept函数<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(l *TCPListener)</span> <span class="title">Accept</span><span class="params">()</span> <span class="params">(Conn, error)</span></span> &#123;</span><br><span class="line">	<span class="keyword">if</span> !l.ok() &#123;</span><br><span class="line">		<span class="keyword">return</span> <span class="literal">nil</span>, syscall.EINVAL</span><br><span class="line">	&#125;</span><br><span class="line">	c, err := l.accept()</span><br><span class="line">	<span class="keyword">if</span> err != <span class="literal">nil</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> <span class="literal">nil</span>, &amp;OpError&#123;Op: <span class="string">"accept"</span>, Net: l.fd.net, Source: <span class="literal">nil</span>, Addr: l.fd.laddr, Err: err&#125;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">return</span> c, <span class="literal">nil</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>Accept内部调用了accept函数，该函数内部实际调用netFD的accept<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(ln *TCPListener)</span> <span class="title">accept</span><span class="params">()</span> <span class="params">(*TCPConn, error)</span></span> &#123;</span><br><span class="line">	fd, err := ln.fd.accept()</span><br><span class="line">	<span class="keyword">if</span> err != <span class="literal">nil</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> <span class="literal">nil</span>, err</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>在net/fd_unix.go中实现了linux环境下accept的操作<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(fd *netFD)</span> <span class="title">accept</span><span class="params">()</span> <span class="params">(netfd *netFD, err error)</span></span> &#123;</span><br><span class="line">	d, rsa, errcall, err := fd.pfd.Accept()</span><br><span class="line">	<span class="keyword">if</span> err != <span class="literal">nil</span> &#123;</span><br><span class="line">		<span class="keyword">if</span> errcall != <span class="string">""</span> &#123;</span><br><span class="line">			err = wrapSyscallError(errcall, err)</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">return</span> <span class="literal">nil</span>, err</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">if</span> netfd, err = newFD(d, fd.family, fd.sotype, fd.net); err != <span class="literal">nil</span> &#123;</span><br><span class="line">		poll.CloseFunc(d)</span><br><span class="line">		<span class="keyword">return</span> <span class="literal">nil</span>, err</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">if</span> err = netfd.init(); err != <span class="literal">nil</span> &#123;</span><br><span class="line">		netfd.Close()</span><br><span class="line">		<span class="keyword">return</span> <span class="literal">nil</span>, err</span><br><span class="line">	&#125;</span><br><span class="line">	lsa, _ := syscall.Getsockname(netfd.pfd.Sysfd)</span><br><span class="line">	netfd.setAddr(netfd.addrFunc()(lsa), netfd.addrFunc()(rsa))</span><br><span class="line">	<span class="keyword">return</span> netfd, <span class="literal">nil</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>上述函数内部调用的是net/fd_unix.go内部实现的Accept函数<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(fd *FD)</span> <span class="title">Accept</span><span class="params">()</span> <span class="params">(<span class="keyword">int</span>, syscall.Sockaddr, <span class="keyword">string</span>, error)</span></span> &#123;</span><br><span class="line">	<span class="keyword">if</span> err := fd.readLock(); err != <span class="literal">nil</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> <span class="number">-1</span>, <span class="literal">nil</span>, <span class="string">""</span>, err</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">defer</span> fd.readUnlock()</span><br><span class="line"></span><br><span class="line">	<span class="keyword">if</span> err := fd.pd.prepareRead(fd.isFile); err != <span class="literal">nil</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> <span class="number">-1</span>, <span class="literal">nil</span>, <span class="string">""</span>, err</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">for</span> &#123;</span><br><span class="line">		s, rsa, errcall, err := accept(fd.Sysfd)</span><br><span class="line">		<span class="keyword">if</span> err == <span class="literal">nil</span> &#123;</span><br><span class="line">			<span class="keyword">return</span> s, rsa, <span class="string">""</span>, err</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">switch</span> err &#123;</span><br><span class="line">		<span class="keyword">case</span> syscall.EAGAIN:</span><br><span class="line">			<span class="keyword">if</span> fd.pd.pollable() &#123;</span><br><span class="line">				<span class="keyword">if</span> err = fd.pd.waitRead(fd.isFile); err == <span class="literal">nil</span> &#123;</span><br><span class="line">					<span class="keyword">continue</span></span><br><span class="line">				&#125;</span><br><span class="line">			&#125;</span><br><span class="line">		<span class="keyword">case</span> syscall.ECONNABORTED:</span><br><span class="line">			<span class="comment">// This means that a socket on the listen</span></span><br><span class="line">			<span class="comment">// queue was closed before we Accept()ed it;</span></span><br><span class="line">			<span class="comment">// it's a silly error, so try again.</span></span><br><span class="line">			<span class="keyword">continue</span></span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">return</span> <span class="number">-1</span>, <span class="literal">nil</span>, errcall, err</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>上述函数就是tcp底层的函数了，accept(fd.Sysfd)监听fd.Sysfd描述符，等待可读事件到来，当可读事件到来后，就可以认为来了一个新的连接，从而创建一个新的描述符给新的连接。<br>当accept出现错误时，需要判断err类型，如果是EAGAIN说明当前没有连接到来，就调用waitRead等待连接，ECONNABORTED说明连接还未accept就断开了，可以忽略。<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(pd *pollDesc)</span> <span class="title">waitRead</span><span class="params">(isFile <span class="keyword">bool</span>)</span> <span class="title">error</span></span> &#123;</span><br><span class="line">	<span class="keyword">return</span> pd.wait(<span class="string">'r'</span>, isFile)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>进而调用pollDesc的wait操作<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(pd *pollDesc)</span> <span class="title">wait</span><span class="params">(mode <span class="keyword">int</span>, isFile <span class="keyword">bool</span>)</span> <span class="title">error</span></span> &#123;</span><br><span class="line">	<span class="keyword">if</span> pd.runtimeCtx == <span class="number">0</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> errors.New(<span class="string">"waiting for unsupported file type"</span>)</span><br><span class="line">	&#125;</span><br><span class="line">	res := runtime_pollWait(pd.runtimeCtx, mode)</span><br><span class="line">	<span class="keyword">return</span> convertErr(res, isFile)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>wait函数中判断pd的runtime上下文是否正常，然后调用runtime包的poll_runtime_pollWait实现挂起等待<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">poll_runtime_pollWait</span><span class="params">(pd *pollDesc, mode <span class="keyword">int</span>)</span> <span class="title">int</span></span> &#123;</span><br><span class="line">	err := netpollcheckerr(pd, <span class="keyword">int32</span>(mode))</span><br><span class="line">	<span class="keyword">if</span> err != <span class="number">0</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> err</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">if</span> GOOS == <span class="string">"solaris"</span> || GOOS == <span class="string">"illumos"</span> || GOOS == <span class="string">"aix"</span> &#123;</span><br><span class="line">		netpollarm(pd, mode)</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">for</span> !netpollblock(pd, <span class="keyword">int32</span>(mode), <span class="literal">false</span>) &#123;</span><br><span class="line">		err = netpollcheckerr(pd, <span class="keyword">int32</span>(mode))</span><br><span class="line">		<span class="keyword">if</span> err != <span class="number">0</span> &#123;</span><br><span class="line">			<span class="keyword">return</span> err</span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>poll_runtime_pollWait运行在内核M线程中，轮询调用netpollblock，所以内核M线程一直在轮询检测netpollblock返回值，当其返回true时循环就可以退出，从而用户态协程就可以继续运行了。<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">netpollblock</span><span class="params">(pd *pollDesc, mode <span class="keyword">int32</span>, waitio <span class="keyword">bool</span>)</span> <span class="title">bool</span></span> &#123;</span><br><span class="line">	gpp := &amp;pd.rg</span><br><span class="line">	<span class="keyword">if</span> mode == <span class="string">'w'</span> &#123;</span><br><span class="line">		gpp = &amp;pd.wg</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="comment">// set the gpp semaphore to WAIT</span></span><br><span class="line">	<span class="keyword">for</span> &#123;</span><br><span class="line">		old := *gpp</span><br><span class="line">		<span class="keyword">if</span> old == pdReady &#123;</span><br><span class="line">			*gpp = <span class="number">0</span></span><br><span class="line">			<span class="keyword">return</span> <span class="literal">true</span></span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span> old != <span class="number">0</span> &#123;</span><br><span class="line">			throw(<span class="string">"runtime: double wait"</span>)</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span> atomic.Casuintptr(gpp, <span class="number">0</span>, pdWait) &#123;</span><br><span class="line">			<span class="keyword">break</span></span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">if</span> waitio || netpollcheckerr(pd, mode) == <span class="number">0</span> &#123;</span><br><span class="line">		gopark(netpollblockcommit, unsafe.Pointer(gpp), waitReasonIOWait, traceEvGoBlockNet, <span class="number">5</span>)</span><br><span class="line">	&#125;</span><br><span class="line">	old := atomic.Xchguintptr(gpp, <span class="number">0</span>)</span><br><span class="line">	<span class="keyword">if</span> old &gt; pdWait &#123;</span><br><span class="line">		throw(<span class="string">"runtime: corrupted polldesc"</span>)</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">return</span> old == pdReady</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>netpollblock内部根据读模式还是写模式，获取pollDesc成员变量的读协程或者写协程地址，然后判断其状态是否为pdReady，这里要详细说一下，golang阻塞一个用户态协程是要将其状态设置为0(正在运行)或者pdWait(阻塞)，这里为0，所以逻辑继续往下走，之后做了一个原子操作将gpp设置为pdWait状态，接着根据这个状态，执行gopark函数，阻塞住用户态协程。当内核想激活用户协程时gopark会返回，然后该函数判断gpp是否为pdReady，从而激活用户态协程。<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">gopark</span><span class="params">(unlockf <span class="keyword">func</span>(*g, unsafe.Pointer)</span> <span class="title">bool</span>, <span class="title">lock</span> <span class="title">unsafe</span>.<span class="title">Pointer</span>, <span class="title">reason</span> <span class="title">waitReason</span>, <span class="title">traceEv</span> <span class="title">byte</span>, <span class="title">traceskip</span> <span class="title">int</span>)</span> &#123;</span><br><span class="line">	<span class="keyword">if</span> reason != waitReasonSleep &#123;</span><br><span class="line">		checkTimeouts() <span class="comment">// timeouts may expire while two goroutines keep the scheduler busy</span></span><br><span class="line">	&#125;</span><br><span class="line">	mp := acquirem()</span><br><span class="line">	gp := mp.curg</span><br><span class="line">	status := readgstatus(gp)</span><br><span class="line">	<span class="keyword">if</span> status != _Grunning &amp;&amp; status != _Gscanrunning &#123;</span><br><span class="line">		throw(<span class="string">"gopark: bad g status"</span>)</span><br><span class="line">	&#125;</span><br><span class="line">	mp.waitlock = lock</span><br><span class="line">	mp.waitunlockf = unlockf</span><br><span class="line">	gp.waitreason = reason</span><br><span class="line">	mp.waittraceev = traceEv</span><br><span class="line">	mp.waittraceskip = traceskip</span><br><span class="line">	releasem(mp)</span><br><span class="line">	<span class="comment">// can't do anything that might move the G between Ms here.</span></span><br><span class="line">	mcall(park_m)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>gopark将用户态协程放在等待队列中，然后调用mcall触发汇编代码。之后会检测调用unlockf函数，如果unlockf返回false则说明可以解锁用户态协程了。另外官网的注释说unlockf不要访问用户态协程的stack，因为G’s stack可能会在gopark和unlockf之间被移除。到目前为止，我们理解了用户态协程挂起原理。</p>
<h2 id="epoll就绪后如何激活用户态协程"><a href="#epoll就绪后如何激活用户态协程" class="headerlink" title="epoll就绪后如何激活用户态协程"></a>epoll就绪后如何激活用户态协程</h2><p>想知道如果激活挂起的用户态协程，就要先看看epoll_wait判断就绪事件后怎么处理的。runtime/netpoll_epoll.go中实现了epollwait逻辑<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">netpoll</span><span class="params">(delay <span class="keyword">int64</span>)</span> <span class="title">gList</span></span> &#123;</span><br><span class="line">	<span class="keyword">if</span> epfd == <span class="number">-1</span> &#123;</span><br><span class="line">		<span class="keyword">return</span> gList&#123;&#125;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">//...</span></span><br><span class="line">	<span class="keyword">var</span> events [<span class="number">128</span>]epollevent</span><br><span class="line">retry:</span><br><span class="line">	n := epollwait(epfd, &amp;events[<span class="number">0</span>], <span class="keyword">int32</span>(<span class="built_in">len</span>(events)), waitms)</span><br><span class="line">	<span class="keyword">if</span> n &lt; <span class="number">0</span> &#123;</span><br><span class="line">		<span class="keyword">if</span> n != -_EINTR &#123;</span><br><span class="line">			<span class="built_in">println</span>(<span class="string">"runtime: epollwait on fd"</span>, epfd, <span class="string">"failed with"</span>, -n)</span><br><span class="line">			throw(<span class="string">"runtime: netpoll failed"</span>)</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="comment">// If a timed sleep was interrupted, just return to</span></span><br><span class="line">		<span class="comment">// recalculate how long we should sleep now.</span></span><br><span class="line">		<span class="keyword">if</span> waitms &gt; <span class="number">0</span> &#123;</span><br><span class="line">			<span class="keyword">return</span> gList&#123;&#125;</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">goto</span> retry</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">var</span> toRun gList</span><br><span class="line">	<span class="keyword">for</span> i := <span class="keyword">int32</span>(<span class="number">0</span>); i &lt; n; i++ &#123;</span><br><span class="line">		ev := &amp;events[i]</span><br><span class="line">		<span class="keyword">if</span> ev.events == <span class="number">0</span> &#123;</span><br><span class="line">			<span class="keyword">continue</span></span><br><span class="line">		&#125;</span><br><span class="line">        <span class="comment">//...</span></span><br><span class="line">		<span class="keyword">var</span> mode <span class="keyword">int32</span></span><br><span class="line">		<span class="keyword">if</span> ev.events&amp;(_EPOLLIN|_EPOLLRDHUP|_EPOLLHUP|_EPOLLERR) != <span class="number">0</span> &#123;</span><br><span class="line">			mode += <span class="string">'r'</span></span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span> ev.events&amp;(_EPOLLOUT|_EPOLLHUP|_EPOLLERR) != <span class="number">0</span> &#123;</span><br><span class="line">			mode += <span class="string">'w'</span></span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span> mode != <span class="number">0</span> &#123;</span><br><span class="line">			pd := *(**pollDesc)(unsafe.Pointer(&amp;ev.data))</span><br><span class="line">			pd.everr = <span class="literal">false</span></span><br><span class="line">			<span class="keyword">if</span> ev.events == _EPOLLERR &#123;</span><br><span class="line">				pd.everr = <span class="literal">true</span></span><br><span class="line">			&#125;</span><br><span class="line">			netpollready(&amp;toRun, pd, mode)</span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">return</span> toRun</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>可以看出netpoll函数调用epollwait返回就绪事件列表，然后遍历就绪的事件列表，从事件类型中取出pollDesc数据，调用netpollready将曾经挂起的协程放入gList中，然后返回该列表<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">netpollready</span><span class="params">(toRun *gList, pd *pollDesc, mode <span class="keyword">int32</span>)</span></span> &#123;</span><br><span class="line">	<span class="keyword">var</span> rg, wg *g</span><br><span class="line">	<span class="keyword">if</span> mode == <span class="string">'r'</span> || mode == <span class="string">'r'</span>+<span class="string">'w'</span> &#123;</span><br><span class="line">		rg = netpollunblock(pd, <span class="string">'r'</span>, <span class="literal">true</span>)</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">if</span> mode == <span class="string">'w'</span> || mode == <span class="string">'r'</span>+<span class="string">'w'</span> &#123;</span><br><span class="line">		wg = netpollunblock(pd, <span class="string">'w'</span>, <span class="literal">true</span>)</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">if</span> rg != <span class="literal">nil</span> &#123;</span><br><span class="line">		toRun.push(rg)</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">if</span> wg != <span class="literal">nil</span> &#123;</span><br><span class="line">		toRun.push(wg)</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>netpollready调用了unblock函数，并且将协程写入glist中<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">netpollunblock</span><span class="params">(pd *pollDesc, mode <span class="keyword">int32</span>, ioready <span class="keyword">bool</span>)</span> *<span class="title">g</span></span> &#123;</span><br><span class="line">	gpp := &amp;pd.rg</span><br><span class="line">	<span class="keyword">if</span> mode == <span class="string">'w'</span> &#123;</span><br><span class="line">		gpp = &amp;pd.wg</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">for</span> &#123;</span><br><span class="line">		old := *gpp</span><br><span class="line">		<span class="keyword">if</span> old == pdReady &#123;</span><br><span class="line">			<span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span> old == <span class="number">0</span> &amp;&amp; !ioready &#123;</span><br><span class="line">			<span class="comment">// Only set READY for ioready. runtime_pollWait</span></span><br><span class="line">			<span class="comment">// will check for timeout/cancel before waiting.</span></span><br><span class="line">			<span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">var</span> <span class="built_in">new</span> <span class="keyword">uintptr</span></span><br><span class="line">		<span class="keyword">if</span> ioready &#123;</span><br><span class="line">			<span class="built_in">new</span> = pdReady</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span> atomic.Casuintptr(gpp, old, <span class="built_in">new</span>) &#123;</span><br><span class="line">			<span class="keyword">if</span> old == pdReady || old == pdWait &#123;</span><br><span class="line">				old = <span class="number">0</span></span><br><span class="line">			&#125;</span><br><span class="line">			<span class="keyword">return</span> (*g)(unsafe.Pointer(old))</span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>netpollunblock函数修改pd所在协程的状态为0，表示可运行状态，所以netpoll函数内部做了这样几件事，根据就绪事件列表找到对应的协程，将挂起的协程状态设置为0表示可运行，然后将该协程放入glist中。在runtime/proc.go中findrunnable会判断是否初始化epoll，如果初始化了则调用netpoll，从而获取glist，然后traceGoUnpark激活挂起的协程<br><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="title">findrunnable</span><span class="params">()</span> <span class="params">(gp *g, inheritTime <span class="keyword">bool</span>)</span></span> &#123;</span><br><span class="line">	_g_ := getg()</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">	<span class="keyword">if</span> netpollinited() &amp;&amp; atomic.Load(&amp;netpollWaiters) &gt; <span class="number">0</span> &amp;&amp; atomic.Load64(&amp;sched.lastpoll) != <span class="number">0</span> &#123;</span><br><span class="line">		<span class="keyword">if</span> list := netpoll(<span class="number">0</span>); !list.empty() &#123; <span class="comment">// non-blocking</span></span><br><span class="line">			gp := list.pop()</span><br><span class="line">			injectglist(&amp;list)</span><br><span class="line">			casgstatus(gp, _Gwaiting, _Grunnable)</span><br><span class="line">			<span class="keyword">if</span> trace.enabled &#123;</span><br><span class="line">				traceGoUnpark(gp, <span class="number">0</span>)</span><br><span class="line">			&#125;</span><br><span class="line">			<span class="keyword">return</span> gp, <span class="literal">false</span></span><br><span class="line">		&#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">//...</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>以上就是golang网络调度和协程控制的原理，golang通过epoll和用户态协程调度结合的方式，实现了高并发的网络处理，这种思路是值得日后我们设计产品借鉴的。<br>感谢关注我的公众号<br><img src="wxgzh.jpg" alt="wxgzh.jpg"></p>

      
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      $.ajax({
        url: path,
        dataType: isXml ? "xml" : "json",
        async: true,
        success: function(res) {
          // get the contents from search data
          isfetched = true;
          $('.popup').detach().appendTo('.header-inner');
          var datas = isXml ? $("entry", res).map(function() {
            return {
              title: $("title", this).text(),
              content: $("content",this).text(),
              url: $("url" , this).text()
            };
          }).get() : res;
          var input = document.getElementById(search_id);
          var resultContent = document.getElementById(content_id);
          var inputEventFunction = function() {
            var searchText = input.value.trim().toLowerCase();
            var keywords = searchText.split(/[\s\-]+/);
            if (keywords.length > 1) {
              keywords.push(searchText);
            }
            var resultItems = [];
            if (searchText.length > 0) {
              // perform local searching
              datas.forEach(function(data) {
                var isMatch = false;
                var hitCount = 0;
                var searchTextCount = 0;
                var title = data.title.trim();
                var titleInLowerCase = title.toLowerCase();
                var content = data.content.trim().replace(/<[^>]+>/g,"");
                var contentInLowerCase = content.toLowerCase();
                var articleUrl = decodeURIComponent(data.url);
                var indexOfTitle = [];
                var indexOfContent = [];
                // only match articles with not empty titles
                if(title != '') {
                  keywords.forEach(function(keyword) {
                    function getIndexByWord(word, text, caseSensitive) {
                      var wordLen = word.length;
                      if (wordLen === 0) {
                        return [];
                      }
                      var startPosition = 0, position = [], index = [];
                      if (!caseSensitive) {
                        text = text.toLowerCase();
                        word = word.toLowerCase();
                      }
                      while ((position = text.indexOf(word, startPosition)) > -1) {
                        index.push({position: position, word: word});
                        startPosition = position + wordLen;
                      }
                      return index;
                    }

                    indexOfTitle = indexOfTitle.concat(getIndexByWord(keyword, titleInLowerCase, false));
                    indexOfContent = indexOfContent.concat(getIndexByWord(keyword, contentInLowerCase, false));
                  });
                  if (indexOfTitle.length > 0 || indexOfContent.length > 0) {
                    isMatch = true;
                    hitCount = indexOfTitle.length + indexOfContent.length;
                  }
                }

                // show search results

                if (isMatch) {
                  // sort index by position of keyword

                  [indexOfTitle, indexOfContent].forEach(function (index) {
                    index.sort(function (itemLeft, itemRight) {
                      if (itemRight.position !== itemLeft.position) {
                        return itemRight.position - itemLeft.position;
                      } else {
                        return itemLeft.word.length - itemRight.word.length;
                      }
                    });
                  });

                  // merge hits into slices

                  function mergeIntoSlice(text, start, end, index) {
                    var item = index[index.length - 1];
                    var position = item.position;
                    var word = item.word;
                    var hits = [];
                    var searchTextCountInSlice = 0;
                    while (position + word.length <= end && index.length != 0) {
                      if (word === searchText) {
                        searchTextCountInSlice++;
                      }
                      hits.push({position: position, length: word.length});
                      var wordEnd = position + word.length;

                      // move to next position of hit

                      index.pop();
                      while (index.length != 0) {
                        item = index[index.length - 1];
                        position = item.position;
                        word = item.word;
                        if (wordEnd > position) {
                          index.pop();
                        } else {
                          break;
                        }
                      }
                    }
                    searchTextCount += searchTextCountInSlice;
                    return {
                      hits: hits,
                      start: start,
                      end: end,
                      searchTextCount: searchTextCountInSlice
                    };
                  }

                  var slicesOfTitle = [];
                  if (indexOfTitle.length != 0) {
                    slicesOfTitle.push(mergeIntoSlice(title, 0, title.length, indexOfTitle));
                  }

                  var slicesOfContent = [];
                  while (indexOfContent.length != 0) {
                    var item = indexOfContent[indexOfContent.length - 1];
                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
                    var start = position - 20;
                    var end = position + 80;
                    if(start < 0){
                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  

  

  
  

  

  

  

</body>
</html>
